CPU 99% + bad write retry - once again

I am using 0.15 from svn with Zope 2.7.6. I used Zope 2.7 installation 
instructions from 0.13 with a small compatibility patch in datatypes.py. 
Client authentication is on. Generally it works fine but every once in a 
while, especially when serving longer pages/content (in particular PDF) 
the CPU load goes up to 99% for ~a minute and then request fails leaving 
"xxx requests: bad write retry". I applied the fix Ng was talking about 
here http://sandbox.rulemaker.net/ngps/199 and here 
https://listserv.surfnet.nl/scripts/wa.exe?A2=ind0501&L=PYTHON-CRYPTO&P=R1100&I=-3 
without success.

Any ideas?

... would be actually very cool to have Zope 2.7 installation package 
back in the distribution...

Thanks!